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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
How much can you SAFELY charge any microwave capacitor? And what is the failure mode? I wouldn't want to have one or two explode on my face, if there is a risk of explosion I'd rather put them in some enclosure...
Registered Member #1407
Joined: Fri Mar 21 2008, 07:09AM
Location:
Posts: 222
Dr. Kilovolt wrote ...
How much can you SAFELY charge any microwave capacitor? And what is the failure mode? I wouldn't want to have one or two explode on my face, if there is a risk of explosion I'd rather put them in some enclosure...
iv read the peak is 8 kv but i think 3kv would be the most you could push them to be 'safe'
Registered Member #396
Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176
I've tested one to 10kv repeatedly (charging and discharging into a short maybe 15-20 times) and it did not fail. But keep in mind that its hard to say if all MOCs are created equally. Steve Ward did so as well for his can crusher bank (which is what I do with them as well). Also, most have an internal resistor (or maybe some just a high leakage resistance - probably not though) that will require you to constantly charge them, and they will dissipate that extra energy as heat.
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I think the statement that not all are created equal is very sage advice. I have a very large number of them and have experimented briefly. I've noticed that certain brands begin to heat and swell at about 2x the rated capacity while others were just fine at close to 3x.
I've seen GE, Sanyo, & Aerovox take a lot of extra energy...while the ones that started to heat and swell were made by a "Sam Hwa" capacitor company and "Norron". While this is NO scientific guideline what so ever, if the construction of the given cap is larger and more robust and made by a larger Japanese firm than a smaller cap of the same rating made in China; I would suggest that the more established manufacturer with the use of stronger larger materials is a better bet for abuse.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
The SAFE voltage rating is the absolute maximum rating written on the case. Thats why it's printed on there!
In practice some capacitors will tolerate 100% over-voltage happily, while others will fail at a level just over the rated voltage. As long as they work at the specified rated voltage you can't complain to the manufacturer, anything above the absolute maximum rating is in unknown territory.
Out of interest some tight tolerance HV capacitors are actually brought into tolerance using a special "self-healing" cell type of arrangement. The capacitor is designed to initially come in above top tolerance. The capacitance is then continually monitored as the applied voltage is increased. This causes breakdown and fuses sections isolating areas of "plate material" until the C value is tuned down to be within tolerance. The voltage required to perform this operation gives some indication to the manufacturer of dielectric quality. If this voltage is suddenly lower one day, they can go searching to see if someone dropped some fag ash into the capacitor rolling machine!
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How much voltage can a microwave cap take?
Thats why it's printed on there!
